Multiple sheet detection system

ABSTRACT

A multiple feed document detection system for use with a document transport for detecting the presence of multiple documents utilizes multiple doubles detection devices wherein each device detects the presence of doubles. The output signals of each device are applied to a comparator which compares the signals obtained from each device. If each device indicates the presence of doubles, then the comparator provides an output that multiple sheets are present. The system thereby eliminates the reading of false doubles by the comparison of the output signals from two or more doubles detection devices.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to document transports, and moreparticularly to a detector for detecting multiple feed sheets.

BACKGROUND OF THE INVENTION

For efficient document processing along a document transport, apreferred method of feeding documents into the transport is via anautomated document feeder. On occasions, however, an automated documentfeeder may feed more than one document at a time. In the event that morethan one document is fed, there is a need to detect that “doubles” ormultiple documents are present.

One system for detecting multiple feed documents is by measuring thethickness of the document. However, in applications of feeding a mixtureof different types of documents, measuring the thickness of thedocuments is not a viable solution. Also, a thickness detector is acontact method of sensing multiple documents and has a disadvantage thatpaper jams can result. The contact method also requires calibrationusing the maximum thickness document that will be fed through thedocument transport.

Another device for detecting multiple feed documents is utilizing avacuum system. In a vacuum system, detection of multiple feed documentsof different thicknesses is possible. A vacuum system is fairlyreliable; however, the vacuum sensors must be placed in close proximityto each side of the document in order to detect multiple feed documents.A vacuum is placed on both sides of the document path. If a single itemis fed, then that item blocks only one vacuum. If two or more documentsare fed simultaneously, then both vacuums are blocked. For an open trackdocument transport, the use of a vacuum doubles detect system is notdesirable. In an open track document transport, a doubles detectionsystem must not interfere with the open track design.

Another contact device for detecting sheet doubles utilizes rollers oneach side of the document path and the rotation of the rollers ismonitored, such as in a magnetic clutch and roller device. One roller,or a set of rollers is controlled by a drive mechanism. The opposingroller or set of rollers, is connected to a mechanical clutch and thespeed of this roller set is controlled by contact with the drivenrollers, or the documents that pass between them. If a single item ispassed between this type of detector, then the opposing rollers willmatch the speed of the driven roller and no multiple sheets aredetected. If two or more sheets are fed simultaneously through thedevice, then the magnetic brake will cause slippage between the multiplesheets, creating a speed mis-match between the opposing rollers and thedriven rollers. Detection of doubles is then realized. However, where achemical reaction occurs between laser printed items and carbonlesscoatings, known as “sticky checks”, the multiple items are gluedtogether, and slippage between the items is not likely to occur.Therefore, a magnetic clutch and roller device is not itself a reliabledevice for detecting doubles.

A non-contact device for multiple document detection utilizes ultrasoundsignals which pass through the document to determine if more than onedocument is present. Sending ultrasound waves through paper results inattenuation of the ultrasound signal. It is possible to determine thepresence of multiple documents by the change in attenuation of thesignal received. An ultrasound detector is independent of the thicknessof the individual documents and detection made without making contactwith these documents. A continuously transmitted sonic wave causesvibrations in the first sheet which is then transmitted via theintervening air to the second sheet, which also begins to vibrate. Thereceiver unit of an ultrasonic detection system is able to detect theseweakened signals via the air. While an ultrasonic multiple documentdetector can accurately detect doubles even if the documents are stucktogether, a disadvantage of such detectors is that the apparatus willregister a false positive when items such as envelopes are fed. Also thepresence of folded corners, sometimes known as “dog ears”, will yield afalse positive.

A need has arisen for a document doubles detection system.

SUMMARY OF THE INVENTION

In accordance with the present invention, a multiple feed documentdetection system for use with a document transport for detecting thepresence of multiple documents is provided. The system utilizes multipledoubles detection devices wherein each device detects the presence ofdoubles. The output signals of each device are applied to a comparatorwhich compares the signals obtained from each device. If each deviceindicates the presence of doubles, then the comparator provides anoutput that multiple sheets are present. The present system therebyeliminates the reading of false doubles by the comparison of the outputsignals from two or more doubles detection devices.

BRIEF DESCRIPTION OF THE DRAWING

For a more complete understanding of the present invention and forfurther advantages thereof, reference is now made to the followingDescription of the Preferred Embodiments taken in conjunction with theaccompanying Drawing which is a block diagram of the present system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the FIGURE, the present multiple sheet detection system isillustrated, and is generally identified by the numeral 10. System 10includes an ultrasonic detection device 12 which provides a first outputsignal 14 indicating the presence of multiple sheets and a second outputsignal 16 indicating that no multiple sheets are detected. Ultrasonicdetection device 12 may include, for example, devices described andshown in U.S. Pat. Nos. 4,066,969 and 6,511,064, which descriptions arehereby incorporated by reference. Signals 14 and 16 are applied to acomparator 18 whose operation will be subsequently described.

Detection system 10 further includes a magnetic clutch and rollerdetection device 20. Detection device 20 generates a first signal 22indicating the presence of multiple documents, and a second signal 24indicating that no multiple documents are present. Signals 22 and 24 areapplied to comparator 18. Clutch and roller detection device 20 maycomprise, for example, the device described and shown in U.S. patentapplication Ser. No. 10/962,739 filed Oct. 12, 2004, which descriptionis hereby incorporated by reference.

Detection system 10 further includes a sheet thickness detection device30. Detection device 30 generates a first output signal 32 indicatingthe presence of multiple documents, and a second output signal 34indicating that no multiple documents are present. Signals 32 and 34 areapplied to comparator 18. Detection device 30 may comprise, for example,a device such as that described in U.S. Pat. No. 5,204,537, whichdisclosure is hereby incorporated by reference.

A fourth doubles detection device is included within detection system 10and includes a vacuum sheet separator detection device 40. Vacuumdetection device 40 applies a vacuum to both sides of a documenttransport and generates a first output signal 42 indicating the presenceof multiple documents, and a second signal 44 indicating that nodocument doubles are present. Signals 42 and 44 are applied tocomparator 18.

Comparator 18 receives the output signals of each detection device 12,20, 30 or 40 utilized within detection system 10. Comparator 18functions to generate a multiple sheet present signal 52 or a multiplesheet not present signal 54. Comparator 18 functions to determinewhether two or more first signals generated by a detection device 12,20, 30 or 40 are present. The presence of two document doubles signalsare required in order to generate a multiple sheet present signal 52.Because detection system 10 utilizes two or more detection devices 12,20, 30 or 40, a false doubles indication by one detection device willnot result in a multiple sheet present signal. For example, when anenvelope passes through ultrasonic detection device 12, first signal 14will typically be generated, but will be a false doubles indication.When utilizing detection device 10 with a thickness detection device 30,where no doubles detection occurs for the envelope, since the output ofthe thickness device 30 will produce signal 34, the output of comparator18 will indicate that multiple sheets are not present by generatingsignal 54. System 10 may utilize any combination of detection devices12, 20, 30 or 40, so long as two or more devices are utilized in orderto compare the data output of each detection device with that of anotherdetection device.

Other alteration and modification of the invention will likewise becomeapparent to those of ordinary skill in the art upon reading the presentdisclosure, and it is intended that the scope of the inventionsdisclosed herein be limited only by the broadest interpretation of theappended claims to which the inventors are legally entitled.

1. A system for detecting the presence of multiple sheets moving along apath, the system comprising: a first doubles detection device disposedat a first position along the path, said first doubles detection devicegenerating a first output signal upon detection of multiple sheets and asecond output signal upon detection of a single sheet at the firstposition; a second doubles detection device disposed at a secondposition along the path, said second doubles detection device generatinga first output signal upon detection of multiple sheets and a secondoutput signal upon the detection of a single sheet at the secondposition; and a comparator for receiving said output signals of saidfirst and said second doubles detection devices and for generating anoutput signal indicating the presence of multiple documents along thepath when said first output signal of said first doubles detectiondevice and said first output signal of said second doubles detectiondevice are present.
 2. The system of claim 1 wherein said first doublesdetection device includes an ultrasonic detection device.
 3. The systemof claim 2 wherein said second doubles detection device includes aclutch and roller detection device.
 4. The system of claim 2 whereinsaid second doubles detection device includes a thickness detectiondevice.
 5. The system of claim 2 wherein said second doubles detectiondevice includes a vacuum detection device.
 6. A system for detecting thepresence of multiple sheets moving along a path, the system comprising:an ultrasonic detection device disposed at a first position along thepath, said ultrasonic doubles detection device generating a first outputsignal upon detection of multiple sheets and a second output signal upondetection of a single sheet at the first position; a first doublesdetection device disposed at a second position along the path, saidfirst doubles detection device generating a first output signal upondetection of multiple sheets and a second output signal upon detectionof a single sheet at the second position; a second doubles detectiondevice disposed at a third position along the path, said second doublesdetection device generating a first output signal upon detection ofmultiple sheets and a second output signal upon the detection of asingle sheet at the third position; and a comparator for receiving saidoutput signals of said ultrasound detection device and said first andsaid second doubles detection devices and for generating an outputsignal indicating the presence of multiple documents along the path whensaid first output signals of said doubles detection devices are present.7. The system of claim 6 wherein said first doubles detection deviceincludes a thickness detection device and said second doubles detectiondevice includes a clutch and roller detection device.
 8. The system ofclaim 6 wherein said first doubles detection device includes a thicknessdetection device and said second doubles detection device includes avacuum detection device.
 9. The system of claim 6 wherein said firstdoubles detection device includes a clutch and roller detection deviceand said second doubles detection device includes a vacuum detectiondevice.